Exception

Descendants of class Exception are used to
communicate between Kernel#raise
and rescue statements in begin ... end blocks. Exception objects carry information about the
exception – its type (the exception's class name), an optional
descriptive string, and optional traceback information. Exception subclasses may add additional
information like NameError#name.

Programs may make subclasses of Exception,
typically of StandardError or RuntimeError, to provide custom classes and
add additional information. See the subclass list below for defaults for
raise and rescue.

When an exception has been raised but not yet handled (in
rescue, ensure, at_exit and
END blocks) the global variable $! will contain
the current exception and $@ contains the current
exception's backtrace.

It is recommended that a library should have one subclass of StandardError or RuntimeError and have specific exception types
inherit from it. This allows the user to rescue a generic exception type
to catch all exceptions the library may raise even if future versions of
the library add new exception subclasses.

Public Class Methods

exception(string) → an_exception or excclick to toggle source

With no argument, or if the argument is the same as the receiver, return
the receiver. Otherwise, create a new exception object of the same class as
the receiver, but with a message equal to string.to_str.

With no argument, or if the argument is the same as the receiver, return
the receiver. Otherwise, create a new exception object of the same class as
the receiver, but with a message equal to string.to_str.